Hydrophobic Surface Modified Aluminas for Polymer Compositions and Method for Making Thereof

ABSTRACT

A method of producing new hydrophobic aluminas by
         i) providing a slurry comprising an alumina compound, the slurry having a pH of above 5.5;   ii) mixing an organic composition comprising carboxylic acids with long hydrocarbon chains with the slurry to form an acid modified slurry;   iii) hydrothermally conditioning the acid modified slurry to form a hydrothermally aged slurry; and   iv) drying the hydrothermally aged slurry.       

     The new hydrophobic aluminas have surface modified structures distinguished by a low humidity content and very small nanoparticles. These new hydrophobic aluminas can be uniformly dispersed in a substrate, for example polymers.

THE INVENTION relates to a novel method for producing a hydrophobicalumina, to a new hydrophobic alumina, and to a composition comprisingthe new hydrophobic alumina and a substrate.

BACKGROUND

Polymers are widely used for several applications, for example, toproduce fibers, films or various coating materials. Thermoplastics arethe most widely used in industry. Polymers are often used as or inbarriers, e.g., films, adhesives, or the like, to improve properties andperformance of various materials.

In the field of barrier polymers, complex processes and technologies,not particularly efficient in terms of energy, are applied to achieveresistance towards molecular permeation (e.g., multilayer films orpolymer blends are employed).^([1])

Materials with ultrahigh oxygen barrier properties over a large humidityrange are obtained by combining high oxygen barrier polymers and watersensitive barriers (ethylene vinyl alcohol copolymer) with at least twolayers of relatively high hydrophobic polymers (polyethylene, “PE”).Polymer blends can also be used in the field of barrier polymers as theblend(s) can achieve properties that cannot be obtained with a singlelayer of polymer.

The use of inorganic particles in polymeric materials to improve variousproperties is well known in the art. For example, clays have beenstudied to a significant extent as fillers for polymers, as reinforcingagents, and as barrier materials. A great variety of methods examinedattest to the fact that the final physical properties and theperformance of the materials depend strictly on the manufacturingtechniques, the preparation methods, and the possibility to exfoliatethe filler material. However, use of mined clays, exfoliated ordispersed to single particles, has become a major technologicalchallenge.^([2-5])

The use of mined clays has some disadvantages. This is because they maycontain minerals that adsorb a considerable amount of humidity. Evenafter removing humidity by heating at high temperature, in most cases,the humidity is readily regained at room temperature, making the use ofsuch clays more complicated. Efficient exfoliation of platelets to formfully dispersed, single particle morphologies can be hindered by thefact that clay particles are hydrophilic, and many polymers of interestare hydrophobic (e.g., polyethylene terephthalate “PET”, polyethylene“PE”, polypropylene “PP”, etc.).^([1])

There are numerous reports in the literature about improvements andparticle treatments with quaternary ammonium surfactants in order toenable processing of clay into polymers. These materials can modify thehydrophilic character of clay particles through a mechanism ofelectrostatic interaction, and improve the dispersability and wetting inthe host polymer. In doing so, they can provide reinforcement, in somecases via crosslinking. However, it is also reported that such ammoniumsurfactants may decompose during processing in the melt at relativelyhigh temperatures, with negative effects on the durability aspects ofthe polymer^([2,3])

Often the preparation of clay-modified polymers is carried out in thepresence of compatibilizers (such as maleic anhydride) and/or a shortchain metal stearate, which have properties of water repellence.However, metal stearates behave as lubricants and simply surround theparticles without forming a specific chemical bond. Metal stearates andsilanes assist in suspending the clay particles with only a small risein the melt viscosity. However, with nano sized particles onlyagglomerates are incorporated into the polymer matrix with poordispersion, and the material behaves as a conventional filler.^([4])

The use of mechanical techniques to incorporate particles, without anyspecific surface modification, has also been described in the prior art.These treatments are rarely used. An example being kaolin, which cannotbe surface modified. The prior art teaches^([5]) that plate-structuredkaolin that is prepared through a crusher may improve barrierperformance beyond standard latex coatings. Scanning electron microscope(SEM) micrographs of the coating substrate indicate that particles mustbe present at high concentration in order to achieve the desiredproperties. Mined minerals containing large size kaolin crystals arereported to be selectively mined and crushed to micron size plate-likeparticles. The limits achieved to control the thickness of the particlesare on the scale of about 100 nm while the size is above 500 nm (too bigto be effective), therefore highly inefficient with respect to thevolume fraction used.

The high filler volume fraction is expected to enhance the barrierproperties, but conversely, deteriorates the polymer mechanicalcharacteristics.

The literature reports the use of hydrated alumina for polymers withoutmodification of its surface.^([6]) The application relates to polyamideresins being embedded into a particulate for barrier properties. In thisprocess transitional aluminum oxide is obtained by thermal calcinationat high temperature, calcination being carried out at a temperaturegreater than 400° C. The maximum calcination temperature may be lessthan 1050° C. or 1100° C. These temperatures usually result in asubstantial proportion of gamma and theta phase alumina. The process forthe preparation of these materials uses seeds, which sometimes are usedto control crystal growth. The property of this material is claimed tobe derived from the alteration of boehmite with transitional alumina (toavoid forming tight, dense, assemblies of particles). However, it may beargued that the product preparation is made additionally complex by thenecessity of calcination, followed by additional drying of the materialsagain, before addition into polymer. Examples show particles with thesmallest crystal size above 50 nm (or “such as at least 75 nm, such asat least 100 nm, or at least about 135 nm”), generically referring tothe property of this alumina.

BACKGROUND REFERENCES

-   [1] Timothy V. Duncan, Applications of nanotechnology in food    packaging and food safety: Barrier materials, antimicrobials and    sensors, Journal of Colloid and Interface Science 363 (2011) 1-24-   [2] M. D. Sanchez-Garcia, Novel PET Nanocomposites of Interest in    Food Packaging Applications and Comparative Barrier Performance With    Biopolyester Nanocomposites, JOURNAL OF PLASTIC FILM & SHEETING,    VOL. 23-APRIL 2007.-   [3] By Dintcheva, N. Tz.; Al-Malaika, S.; La Mantia, F. P., Effect    of extrusion and photo-oxidation on polyethylene/clay    nanocomposites, Polymer Degradation and Stability (2009), 94(9),    1571-1588.-   [4] Gupta, Kernmel and Kin, Polymer Nanocomposites handbook, CRC    Press.-   [5] IMERYS TECHNICAL GUIDE, Barrisurf T M.-   [6] D. O. Yener, O. Guiselin, R. Bauer, U.S. Pat. No. 8,575,255,    Saint-Gobain Ceramics and Plastics, 2007.

Background references [1]-[6] are incorporated herein by reference forall purposes.

SUMMARY OF THE INVENTION

The present invention aims to produce, by a simple process, newhydrophobic aluminas having surface modified structures distinguished bya low humidity content and very small nanoparticles. These newhydrophobic aluminas can be uniformly dispersed in a substrate, forexample polymers.

According to a first aspect of the invention there is provided a methodof producing a hydrophobic alumina comprising the steps of:

-   -   i) providing a slurry comprising an alumina compound, the slurry        having a pH of above 5.5;    -   ii) mixing an organic composition comprising carboxylic acids        with long hydrocarbon chains with the slurry to form an acid        modified slurry;    -   iii) hydrothermally conditioning the acid modified slurry to        form a hydrothermally aged slurry; and    -   iv) drying the hydrothermally aged slurry.

The alumina compound includes an aluminum oxide hydroxide (AlOOH), aboehmite or a pseudoboehmite, preferably a boehmite. The aluminum oxidehydroxide may be derived from water hydrolysis of an aluminum alkoxide,or from other alumina sources such as a sodium aluminate source, an alumsource, or numerous other variations.

More particularly, the alumina compound suitable for the method of thepresent invention may be obtained from hydrolysis of aluminum alkoxide.

The aluminum oxide hydroxide is made up of different shaped crystalsincluding hexahedral, tablet-like, block-like, plate-like structures, orcombinations thereof. It preferably has a plate-like or block-likestructure or combinations thereof.

The slurry is preferably an aqueous slurry. In a more preferredembodiment of the invention the aqueous slurry comprising the aluminacompound is an intermediate stream of the Ziegler industrial productionof AlOOH from the hydrolysis of aluminum alkoxide.

The aqueous slurry preferably has a pH of above 5.5, preferably a pH of7.0 to 10.0, more preferably a pH of 8.0 to 10.0.

The organic composition comprises a matrix of long chain fatty acids,hydroxy fatty acids, unsaturated or saturated, poly acids (e.g., citricacid), interlinked chains of the above, and esters. The organiccomposition has a carboxylic acid functional group with long hydrocarbonchains which binds to the surface of the alumina compound.

The organic composition comprises carboxylic acids with hydrocarbonchains having a carbon chain length greater than 10, preferably a carbonchain length between 12 and 24, more preferably 12 and 20 and mostpreferably 14 and 18.

The method of dispersing inorganics throughout the polymeric materialsin the prior art is generally accomplished by extrusion and othermechanical high shear processes. It is not required to utilize such highmechanical energy to produce the positive effects of the presentinvention. On a small scale, the claimed process can be applied in avessel provided with an anchor type impeller which can operate at lowtip speed velocity. For large scale, the process can be carried out in avessel equipped with a mechanical impeller at suitable controlled tipspeed velocity and provided with suitable internal distributors.

The method steps of the invention are important as the organiccomposition is first mixed with an aqueous slurry including the aluminacompound to form an acid modified slurry, such that the organiccomposition dissolves. This is followed by a hydrothermal conditioningor aging step which ensures that the organic composition is effectivelyemulsified with particles of the alumina compound i.e. a hydrothermallyaged slurry that contains finely sub-divided alumina particles isobtained.

It is preferred that the aqueous slurry and the acid modified slurryhave a pH of 7 and above. In certain instances, a pH of 7 or above 7 ismaintained by virtue of the pH of the slurry chosen and the amount oforganic composition added to such a slurry. For example, if the organiccomposition is added in requisite quantities to a slurry of anintermediate stream of the Ziegler industrial production of AlOOH fromthe hydrolysis of aluminum alkoxide, the pH of the acid modified slurrywill remain above 7. In other cases, in order to ensure that the pH ofthe acid modified slurry is maintained at 7 or above 7, the method ofthe invention may include a step of adding a basic solution to the acidmodified slurry, for example NH₄OH. Alternatively, the base can be addedto the slurry before the addition of the organic composition.

By following an embodiment of the invention, the alumina compound isadded to an aqueous suspension, for example water, to form a roomtemperature slurry. The room temperature slurry is introduced into avessel, and a predetermined amount of an organic composition comprisingcarboxylic acids with hydrocarbon chains as defined by the presentinvention is added to the slurry. The organic composition can be addedto the slurry before the slurry is heated. On the other hand, the slurrycan first be heated above ambient temperature, up to a temperature ofabout 200° C., and then mixed with the organic composition. Thoseskilled in the art may also find an alternative suitable way to mix thereagents. For example, in a batch process, the organic composition canbe added to a pre-heated vessel, and the slurry can be added thereafter,or the organic composition can be added simultaneously with the slurry.It is preferred that the aqueous slurry and the acid modified slurryhave a pH of 7 and above. Afterwards, the acid modified slurry undergoesa hydrothermal conditioning treatment to form a hydrothermally agedslurry

The hydrothermal conditioning treatment is performed at a temperaturebetween 90° C. to 200° C. The heat can be supplied through an externalsource (e.g. electrical or via circulating oil in external jacket) orthrough direct injection of high pressurized steam.

The resultant hydrothermally aged slurry is maintained at thetemperature of the hydrothermal conditioning for a period of time thatdepends mainly on the temperature and agitation. Generally speaking, theduration of such hydrothermal aging can be between 1 hour and 6 hours.During the hydrothermal aging concomitant growth of the alumina crystalparticles occurs to provide for specialized morphologies.

At the end of the hydrothermal conditioning or aging, the hydrothermallyaged slurry enters a drying chamber where the hydrothermally aged slurryis dried and a hydrophobic alumina powder is obtained.

The hydrothermally aged slurry may be dried in a spray dryer or acontact dryer, operated with nitrogen or air, but other dryers that canoperate under appropriate temperature can be used. If drying is carriedout with a spray dryer, the atomizer inlet temperature is greater thanabout 200° C. and the atomizer outlet temperature is about 95° C. to140° C., preferably 100° C. to 110° C. With a contact dryer where theheat exchange is conducted through a circulating oil externally to thedryer, the temperature 220-230° C. ° of the oil is about 220-230° C.while the outlet temperature of nitrogen is above 100° C., for exampleabout 112-116° C.

As known in the art, the distribution of particle sizes and the bulkdensity of the powder is fairly constant for a given method of drying.The density can be varied from as little as 0.2 g/cc to as large as 1.0g/cc.

After drying, a hydrophobic alumina powder is obtained in which theorganic composition is anchored to the alumina surface through theAl-carboxylate species. This was verified from the diffuse reflectanceinfrared fourier transform (DRIFT) spectra, by the appearance of theband at 1580 cm⁻¹.

The production of such hydrophobic powders occurs via the formation ofhydrophobic Al-carboxylate species on a surface of the alumina crystalparticles through the reaction of hydroxyl groups and elimination ofsurface water. Due to the lipophilic characteristic of the aluminasurface after the treatment stage, drying results in substantially lowhumidity of the powder to zero humidity content.

Due to the method of surface treatment, covalently bonded organicmolecules form a surface on top of alumina nano crystal particles withdiffering properties as compared to a non-treated polar alumina surface.The surface is comparable to that of the low surface energy polymericsystems which are low surface energy materials. The advantage is thatthe agglomerate strength of the particles is similar to polymer thus itis possible to easily break up the agglomerates and to achieve a uniformdispersion of single nano crystal particles in a polymer.

The hydrophobic alumina powder produced by the method of the presentinvention has a substantially low humidity content. In particular, thehydrophobic alumina powder has less than 3% free water, preferably lessthan 2% free water, more preferably less than 1% free water, even morepreferably less than 0.5% free water, and most preferably less than 0.4%free water. The free water is measured by Karl Fischer orthermogravimetric analysis (TGA) techniques, both known to a personskilled in the art of the invention.

The hydrophobic alumina powder is observed to have a significanthomogeneous surface coated by the organic molecules with remarkable lowwettability by water or polar molecules this in turn has a dramaticimpact in preventing water re-hydration.

The higher the temperature of the drying process, the more coated arethe crystal particles with the Al-carboxylate species, and the lower thehumidity of the final powder, and the more hydrophobic are theparticles.

According to a second aspect of the invention there is provided ahydrophobic alumina prepared according to the method of the invention.

These new hydrophobic aluminas can have specialized aspect ratios. Suchbenefits can confer an advantage at high vol. % loadings pertaining tothermal conductivity, mechanical properties (particularly in the casefor substantially agglomerate-free dispersions in the polymer), or flameretardancy. Conversely, compositions of polymers and these hydrophobicaluminas in lower vol. % loadings make such polymers particularlyresistant to gas permeability for barrier property benefits in filmsand/or in adhesive layers, while still possessing beneficial physicaland mechanical properties.

These characteristics can provide advantages to polymers in terms ofboth performance and higher efficiency, as explained later herein.

The hydrophobic alumina may be comprised of hexahedral, tablet-like,plate-like, block-like or structures or combinations thereof. Preferablythe hydrophobic alumina has a plate-like or block-like structure, orcombinations thereof.

The structure of these crystal particles is measured by X-raydiffraction. The structure of crystals is described by sizes derived indirections along lines perpendicular to the planes of the X-raydiffraction patterns by using the Scherrer formula.

For example, crystal size information to describe the crystal habit ofthe hydrophobic alumina is supplied from X-ray diffraction peaks ofplanes (200), (020), and (002). The size is derived in the directionperpendicular to the measured diffraction planes.

FIG. 6 is an idealized drawing of a crystal particle. The plane (020) isshowed along with the (200), (020) and (002) sizes.

The (020) size is taken as a direct indication of the average thicknessof the crystals. An aspect ratio can be derived among the (002) and the(020) planes.

For block like crystals, the aspect ratio is substantially 1.5:1 to 1:1,plate crystals particles may be characterized by aspect ratios higherthan 1.5:1 to aspect ratios of about 5:1, ultra small plates havethicknesses of about 3-4 nm.

The microstructure of these crystalline solids is also investigated bytransmission electron microscopy (TEM). The information from TEM iscoupled with the x-ray experiment results to have a comparison of theanisotropy using Scherrer relation on (020) lines.

The crystal growth can be changed with the use of an organic compositioncomprising aliphatic carboxylic acid hydrocarbons having a specificchain length of greater than 10 binding to a surface of the aluminacompound for example to manipulate the morphologies of the crystals. Itis known that boehmite crystal particles bear hydroxyl groups on theirsurfaces and thus tend to form bonds with the carboxylic acid. Theorganic composition is characterized by highly hydrophobic molecules andtends to sterically stabilize the crystal by attaching to the hydroxylgroups on the surface of the boehmite crystal particle via thecarboxylic moiety. This treatment aims to modify in particular the basalfaces of the crystals (020) because these surfaces present less sterichindrance for assembly of the organic molecules. The chemistry andmechanism behind this technique is to obtain new crystallitemorphologies. The method of the present invention makes it possible tochange the crystal particle size with ligands that link to the surfaceof the basal faces and thus modify the interfacial surface energy andwettability with water.

When properly controlled, this method can be used to obtain specializedmorphologies. Altering surfaces of alumina with a hydrophobic ligandthat makes growth conditions more favorable in specific directions isthe advantage of the process of the present invention.

During the synthesis process, with hydrothermal treatment conditions ofthe slurry at temperatures preferentially above 100° C., the width andthe length of crystals will increase in relation to the thickness, suchthat increased plate-like crystallites are formed retaining their finalhydrophobic properties.

These new hydrophobic aluminas can be particularly advantageous forforming compositions with substrates such as polymers, especially thosereferred to as non-polar polymers.

According to a third aspect of the invention there is provided acomposition including a hydrophobic alumina prepared according to themethod of the invention and a substrate, the hydrophobic alumina beingdispersed in the substrate.

The substrate comprises polymer, paraffin or oil, more preferablypolymer or paraffin.

The polymer may include a low molecular weight polymer, or a wax.

The particles of the hydrophobic alumina can be dispersed in thesubstrate from 3.5 nano meters to 1000 nano meters, more preferably 3.5nano meters to 600 nano meters and most preferably from 3.5 to 75 nanometers, where the single crystal size preferably ranges from 3.5 nm to75 nm. By particles is meant either a single crystal and/or an aggregateof single crystals, for example two single crystals of 4 nm make up a 8nm aggregate. This dispersibility is measured by SEM technique forsolids, e.g. polymers, and dynamic light scattering for liquids, e.g.oil.

The new compositions of the present invention can confer an advantage athigh vol. % loadings pertaining to thermal conductivity, mechanicalproperties (particularly in the case for substantially agglomerate-freedispersions in the polymer), or flame retardancy. Conversely,compositions of polymers and these hydrophobic aluminas in lower vol. %loadings make such polymers particularly resistant to gas permeabilityfor barrier property benefits in films and/or in adhesive layers, whilestill possessing beneficial physical and mechanical properties.

The hydrophobic alumina can be used in melt compounding processesbecause the hydrophobic alumina is thermally stable at typicaltemperatures used in these processes. It can be used in a carrier suchas a low molecular weight polymer, a wax, or a mineral oil, because itcan be dispersed in these systems. Examples of suitable polymers orcarriers are High Density Polyethylene “HDPE”, Low Density Polyethylene“LDPE”, Polypropylene “PP”, PET, and waxes, for example Fisher Tropsch“FT” waxes.

As the hydrophobic aluminas do not degrade, they are advantageous overother modifiers that decompose at low temperature (e.g., some silanes),and not obvious in polymer processing. The product of the presentinvention is thermally stable under a broad range of compoundingconditions.

In the context of the current invention, a dispersion is a “system ofdispersed particles suspended in a solid, liquid, or gas” or “smallparticles distributed in a fluid”.

The invention will now be described with reference to the followingFigures and non-limiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures:

FIG. 1 is a TGA/DTA analysis of a new hydrophobic alumina as per Example1;

FIG. 2 is a DRIFT spectra of the hydrophobic alumina in Example 1 withthe characteristic Al-carboxylate signal;

FIG. 3 is an SEM that shows the structure of HDPE (high densitypolyethylene) film that contains the hydrophobic alumina of Example 1dispersed to a dimension comparable to single crystal particles.

FIG. 4 is a graph showing surface energy of the hydrophobic alumina ofExample 1 vs an unmodified powder; and

FIG. 5 is a graph showing the wettability of the hydrophobic alumina ofExample 1 vs an unmodified alumina.

FIG. 6 is an idealized drawing of a crystal particle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

This example is a preparation of the hydrophobic alumina of the presentinvention, specifically a hydrophobic boehmite, using an organiccomposition including a carboxylic acid having a carbon chain of 18. Ahydrothermally treated boehmite slurry from a hydrolysis process ofaluminum alkoxide (295 lbs.) at pH value of about 9, was mixed with 4.1lb. of the organic composition including a carboxylic acid having acarbon chain of 18 (17% wt.) to form an acid modified slurry. The acidmodified slurry was hydrothermally treated at 105° C. for 2 hours underlow agitation. After 2 hours of mixing a low viscosity hydrothermallytreated slurry that contained finely sub-divided particles was obtained.The hydrothermally treated slurry (having a pH of between 7 and 7.5) wascooled and pumped at room temperature to a contact dryer operated undernitrogen, which had an external circulating oil jacket that operated at240° C. and where the temperature of the gas exiting the dryer was 115°C.

A hydrophobic alumina was obtained with a bulk density of 0.86 g/cc.

The hydrophobic alumina included long hydrophobic carboxylate moleculeson a surface of alumina crystal particles. This is indicative of theimproved compatibility with hydrophobic polymers.

FIG. 1 is the TGA/DTA analysis of the hydrophobic alumina powder. FIG. 1shows that there is less than 0.5% of free water on the hydrophobicalumina powder. As per FIG. 2, the crystal particles by X-ray arecharacterised by a thickness of 35 nm (020) and length of 37 nm (002).

The particles of the hydrophobic alumina were dispersed in HDPE to aparticle size of 45 nano meters. The particle size was detected by SEMand it is essentially consistent with the dimension of a single crystalthat was determined by X-ray diffraction. HDPE was compounded with thehydrophobic alumina powder of Example 1 in a Brabender mixer at 150° C.,60 rpm for 15 minutes. FIG. 3 is an SEM that shows the structure of theHDPE film containing the hydrophobic alumina made of boehmite crystalparticles which were homogeneously dispersed to a dimension comparableto single crystal particles.

The Inverse Gas Chromatography technique was then applied to investigatepowder surface energies (FIG. 4) and wettability properties of thehydrophobic alumina powder (FIG. 5).

The examined powder was placed in the chromatographic column. Carefullyselected probe molecules with known physicochemical properties wereinjected into the column. The retention data obtained enabledcalculation of values describing surface properties.

The total surface energy was evaluated through the contribution of twocomponents:

γ^(T)=γ^(D)+γ^(AB)

γ^(D) is the dispersive component that is related to the non-polarproperty of the surface, γ^(AB) is the polar contribution of thesurface.

The dispersive component of total surface energy was obtained bymeasuring the adsorption with alkane probe molecules having increasingC-chain length: hexane, heptane, octane and nonane.

The polar component of the total surface energy was obtained by the useof polar probe molecules: acetonitrile, acetone, ethanol, ethyl acetateand dichloromethane.

By taking the polar component divided by the total surface energy,γ^(AB)/γ^(T), the wettability profile of the samples was determined. Anon-polar nature of the surface is described by a low wettabilityprofile.

Analysis was carried out by passing different amounts of probe moleculesinto a column to achieve different surface coverages.

Comparing the hydrophobic alumina powder to untreated boehmite, it wasfound that the hydrophobic alumina modified with the organic modifier ofExample 1 is significantly lower in surface energy, confirming that themodification has a significant impact. The low surface energy value alsocorroborates the lower affinity for polar substances. This is alsohighlighted by the lower wettability profile, thus showing this sampleis compatible with non-polar systems. The lipophilic character of thehydrophobic alumina is verified in a typical non polar liquid, analiphatic mineral oil having a viscosity of 19 cP at 20° C. The powderwas mixed at 10 phr with 90 phr of oil. The resulting dispersion wascentrifuged and the solid residue on the bottom of the centrifuge tubewas weighed after rinsing in hexane and drying at 110° C. The % wt. ofparticles dispersed calculated by difference with respect to the totalamount of powder was 96% wt.

Comparative Example 1

A comparative example using a fatty acid composition having a carbonchain of equal to 8 was carried out. 2500 grams of boehmite solutionfrom a hydrolysis process of aluminum alkoxide at pH value of about 9,was mixed with 180 grams of water. Subsequently 18 grams of octanoicacid were introduced to obtain a number of moles on boehmite in therange of that applied in the Example 1. Then an ammonia solution at30-33% wt, in an amount equal to 9.5 grams, was added under stirring.The resulting slurry was kept at constant agitation at 105° C. for 2hours. The hydrothermally aged slurry was cooled at room temperature,the pH value of the hydrothermally aged slurry was 8.6. Thehydrothermally aged slurry was pumped into a spray atomizer thatoperates with N2 flow to obtain a dry powder. The powder was added to analiphatic oil under the same conditions of Example 1. During mixing timethe viscosity increases considerably until the system exhibited no flow.The test was stopped as the powder was not dispersible in oil.

Although specific embodiments of the invention have been describedherein in some detail, this has been done solely for the purposes ofexplaining the various aspects of the invention, and is not intended tolimit the scope of the invention as defined in the claims which follow.Those skilled in the art will understand that the embodiment shown anddescribed is exemplary, and various other substitutions, alterations andmodifications, including but not limited to those design alternativesspecifically discussed herein, may be made in the practice of theinvention without departing from its scope.

1. A hydrophobic alumina comprising: an alumina compound including analuminum oxide hydroxide (AlOOH), a boehmite, or a pseudoboehmite, saidalumina compound having hydrocarbon chains having a carbon chain lengthof between 12 and 24 carbon atoms formed on the surface thereof; thehydrophobic alumina having a free water content of less than 2.00%. 2.The hydrophobic alumina of claim 1, wherein the hydrophobic alumina hasa final free water content of less than 1.00%.
 3. The hydrophobicalumina of claim 1, wherein the hydrophobic alumina has a final freewater content of less than 0.5%.
 4. The hydrophobic alumina of claim 1,wherein the hydrocarbon chains are covalently bonded to the aluminacompound.
 5. A composition comprising a hydrophobic alumina as claimedin claim 1 and a substrate, the hydrophobic alumina being dispersed inthe substrate.
 6. The composition as claimed in claim 5, wherein thesubstrate is a polymer or a paraffin.
 7. The composition as claimed inclaim 6, wherein the polymer includes a low molecular weight polymer ora wax.
 8. The composition as claimed in claim 1, wherein particles ofthe hydrophobic alumina are dispersed in the substrate to particle sizesof 3.5 nano meters to 75 nano meters.
 9. The composition as claimed inclaim 8, wherein particles of the hydrophobic alumina are dispersed inthe substrate to particle sizes of 3.5 nano meters to 45 nano meters.